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2 Muscles of the Body Skeletal muscles General principles of leverageProduce movementsGeneral principles of leverageMuscles act with or against each otherCriteria used in naming muscles

3 Naming the Skeletal MusclesLocationExample  the brachialis is located on the arm (brachium)ShapeExample  the deltoid is triangularRelative sizeMaximus, minimus, & longus indicate sizeExample  gluteus maximus is the large one & gluteus minimus is the small one

5 Naming the Skeletal MusclesNumber of origins2, 3, or 4 originsIndicated by the words biceps (2), triceps (3), & quadriceps (4)ActionAction can be part of the muscle’s nameIndicates type of muscle movementFlexor, extensor, adductor, or abductor(ie. extensor digitorum)

6 Arrangement of Fascicles in MusclesSkeletal muscles  consist of fasciclesFascicles  arranged in different patternsFascicle arrangement  tells about action of a muscle

7 Arrangement of Fascicles in MusclesTypes of fascicle arrangementParallel  fascicles run parallel to the long axis of the muscleStrap-like  sternocleidomastoidFusiform  biceps brachii

8 Arrangement of Fascicles in MusclesTypes of fascicle arrangementConvergentOrigin of the muscle is broadFascicles converge toward the tendon of insertionExample  Pectoralis major

9 Arrangement of Fascicles in MusclesTypes of fascicle arrangementPennateUnipennate  fascicles insert into one side of the tendonBipennate  fascicles insert into the tendon from both sidesMultipennate  fascicles insert into one large tendon from all sides

10 Arrangement of Fascicles in MusclesCircularFascicles are arranged in concentric ringsSurround external body openingsSphincter  general name for a circular muscleExamplesOrbicularis oris & orbicularis oculi

16 Lever Systems: Bone-Muscle RelationshipsFirst-class leverEffort applied at one endLoad is at the opposite endFulcrum is located between load & effort(a) First-class leverArrangement of the elements isload-fulcrum-effort.LExample: scissorsLoadFulcrumEffortIn the body: A first-class lever systemraises your head off your chest. Theposterior neck muscles provide the effort;the atlanto-occipital joint is the fulcrum;and the weight to be lifted is the facialskeleton.

17 Lever Systems: Bone-Muscle RelationshipsThird-class leverEffort is applied between the load & fulcrumWork speedilyAlways at a mechanical disadvantage(c) Third-class leverArrangement of the elements isload-effort-fulcrum.LExample: tweezers or forcepsFulcrumLoadEffortIn the body: Flexing the forearm by thebiceps brachii muscle exemplifiesthird-class leverage. The effort is exertedon the proximal radius of the forearm; thefulcrum is the elbow joint; and the load isthe hand and distal end of the forearm.

18 Embryonic Development of the MusclesMuscles organized into 4 groupsMusculature of the visceral organsPharyngeal arch musclesAxial musclesLimb muscles

19 Embryonic Development of the MusclesMusculature of the visceral organsIncludes smooth & cardiac muscleDevelops from splanchnic mesodermPharyngeal arch musclesIncludesSkeletal muscles of the pharynxMuscles of the head & neckDevelop from the 4th to 7th somitomeres

20 Development of the MusclesFirst (occipital)myotomesSomitomeresEyePharynxLimb budMyotomesLimb bud(a) 6-week embryo

28 Muscle Actions & Interactions(a) A muscle that crosses on the anterior side ofa joint produces flexion*(b) A muscle that crosses on the posterior side ofa joint produces extension*Example:Latissimus dorsi(posterior view)Example:Pectoralis major(anterior view)*These generalities do not apply to the knee and ankle because the lower limbis rotated during development. The muscles that cross these joints posteriorlyproduce flexion, and those that cross anteriorly produce extension.*These generalities do not apply to the knee and ankle because the lower limbis rotated during development. The muscles that cross these joints posteriorlyproduce flexion, and those that cross anteriorly produce extension.

29 Muscle Actions & Interactions(c) A muscle that crosses on the lateral side of ajoint produces abduction(d) A muscle that crosses on the medial side of ajoint produces adductionExample:Medial deltoid(anterolateral view)Example:Teres major(posterolateral view)

33 Muscle Compartments of the ThighPosterior compartment musclesExtend the hip & flex the kneeInnervation is the tibial branch of the sciatic nerve (later)Anterior compartment musclesFlex the hip & extend the kneeInnervation is the femoral nerve (later)Medial compartmentAdduct the thighInnervation is the obturator nerve (later)

38 Muscles of the Head – Facial ExpressionMuscles of facial expressionLie in the face & scalpThin & variable in shapeOften insert in the skin  not on bones(Innervated by cranial nerve VII  the facial nerve)

46 Muscles of the Neck & Vertebral ColumnTrunk extensionDeep muscles of the backMaintain normal curvatures of the spineForm a column from sacrum to the skullErector spinae groupLargest of the deep back muscles

51 Deep Muscles of the Thorax –BreathingDiaphragmMost important muscle of respiration!Flattens as it contractsIncreases the volume of the thoracic cavityHow does this aid in breathing?Innervated by phrenic nerve (your brain controls)